The invention relates to an electrode frame for use in the electrolytic recovery or purification of metals, the frame being made of a thermosplastic synthetic material, preferably polypropylene, and having an upper and a lower horizontal arm and two lateral arms for connecting together the upper and lower horizontal arms. Such an electrode frame is disclosed in German Offenlegungsschrift No. 2,853,672.
In the electrolytic recovery of metals, for example copper, nickel, silver or the like, an anode of an inert material, for example lead, and a cathode on which the metal is to be precipitated are disposed in a common electrolyte. The cathode is here connected with the negative terminal and the anode with the positive terminal of a direct current source. Frequently, the cathode and anode chambers are separated from one another by a diaphragm and circulating pumps are provided to convey the electrolyte into the cathode chamber. The electrodes themselves generally are rectangular plates of different weights, with the weights possibly increasing up to an order of magnitude of 100 kg. Particularly for the cathode the situation is such that initially, at the beginning of the electrolysis process, the cathode is a relatively thin metal starter sheet which then grows in the course of the electrolysis process and likewise reaches weights in the order of magnitude from 50 to 100 kg, sometimes even more.
The described process of electrolytic metal recovery can also be used, with slight modifications, for the electrolytic purification of metals, for example copper, nickel, silver or the like. In this case, the anode is made of the metal to be purified and is immersed together with the cathode in the common electrolyte. During the passage of current, the metal to be purified is precipitated on the cathode with equivalent quantities simultaneously being removed from the anode.
To prevent the electrodes from touching one another and in order to facilitate the exchange of electrodes, the electrodes are generally surrounded by a frame which absorbs the weight of the electrodes and transfers it to the walls of the electrolysis vessel. The frame itself is made of electrolytically nonconductive material, which is necessary since otherwise metal would also precipitate on the frame and, in particular, the cathode would grow to become part of the frame. To complete the separation, a diaphragm cloth is stretched over the frame together with its contents, this cloth being either attached to special fastening devices on the frame or is simply pulled over the frame and the electrodes therein in the manner of a flat tube or bag.
It has been found that these cloths are easily disposed on the frame with too much or too little tension. This is also due to the fact that during the duration of use of the electrode frames, these cloths change in consistency. Too much tension is usually the result of cloth shrinkage and causes the weave to become more open. Too little tension may permit, for example, nickel to grow into the cloth so that the plate can no longer be removed from the frame and the stress on the frame now becomes nonuniform. If the covering is formed of a cloth bag, its dimensions must be maintained very accurately during manufacture if the desired cloth tension is to be kept within comparatively close tolerances.